/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.sdk.coders;



import com.bff.gaia.unified.sdk.util.common.ElementByteSizeObserver;

import com.bff.gaia.unified.sdk.values.TypeDescriptor;

import com.bff.gaia.unified.vendor.guava.com.google.common.base.Optional;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.ImmutableList;



import javax.annotation.Nullable;

import java.io.IOException;

import java.io.InputStream;

import java.io.OutputStream;

import java.util.List;



/**

 * A {@link NullableCoder} encodes nullable values of type {@code T} using a nested {@code Coder<T>}

 * that does not tolerate {@code null} values. {@link NullableCoder} uses exactly 1 byte per entry

 * to indicate whether the value is {@code null}, then adds the encoding of the inner coder for

 * non-null values.

 *

 * @param <T> the type of the values being transcoded

 */

public class NullableCoder<T> extends StructuredCoder<T> {

  public static <T> NullableCoder<T> of(Coder<T> valueCoder) {

    if (valueCoder instanceof NullableCoder) {

      return (NullableCoder<T>) valueCoder;

    }

    return new NullableCoder<>(valueCoder);

  }



  /////////////////////////////////////////////////////////////////////////////



  private final Coder<T> valueCoder;

  private static final int ENCODE_NULL = 0;

  private static final int ENCODE_PRESENT = 1;



  private NullableCoder(Coder<T> valueCoder) {

    this.valueCoder = valueCoder;

  }



  /** Returns the inner {@link Coder} wrapped by this {@link NullableCoder} instance. */

  public Coder<T> getValueCoder() {

    return valueCoder;

  }



  @Override

  public void encode(@Nullable T value, OutputStream outStream) throws IOException, CoderException {

    encode(value, outStream, Context.NESTED);

  }



  @Override

  public void encode(@Nullable T value, OutputStream outStream, Context context)

      throws IOException, CoderException {

    if (value == null) {

      outStream.write(ENCODE_NULL);

    } else {

      outStream.write(ENCODE_PRESENT);

      valueCoder.encode(value, outStream, context);

    }

  }



  @Override

  public T decode(InputStream inStream) throws IOException, CoderException {

    return decode(inStream, Context.NESTED);

  }



  @Override

  @Nullable

  public T decode(InputStream inStream, Context context) throws IOException, CoderException {

    int b = inStream.read();

    if (b == ENCODE_NULL) {

      return null;

    } else if (b != ENCODE_PRESENT) {

      throw new CoderException(

          String.format(

              "NullableCoder expects either a byte valued %s (null) or %s (present), got %s",

              ENCODE_NULL, ENCODE_PRESENT, b));

    }

    return valueCoder.decode(inStream, context);

  }



  @Override

  public List<Coder<T>> getCoderArguments() {

    return ImmutableList.of(valueCoder);

  }



  /**

   * {@code NullableCoder} is deterministic if the nested {@code Coder} is.

   *

   * <p>{@inheritDoc}

   */

  @Override

  public void verifyDeterministic() throws NonDeterministicException {

    verifyDeterministic(this, "Value coder must be deterministic", valueCoder);

  }



  /**

   * {@code NullableCoder} is consistent with equals if the nested {@code Coder} is.

   *

   * <p>{@inheritDoc}

   */

  @Override

  public boolean consistentWithEquals() {

    return valueCoder.consistentWithEquals();

  }



  @Override

  public Object structuralValue(@Nullable T value) {

    if (value == null) {

      return Optional.absent();

    }

    return Optional.of(valueCoder.structuralValue(value));

  }



  /**

   * Overridden to short-circuit the default {@code StructuredCoder} behavior of encoding and

   * counting the bytes. The size is known (1 byte) when {@code value} is {@code null}, otherwise

   * the size is 1 byte plus the size of nested {@code Coder}'s encoding of {@code value}.

   *

   * <p>{@inheritDoc}

   */

  @Override

  public void registerByteSizeObserver(@Nullable T value, ElementByteSizeObserver observer)

      throws Exception {

    observer.update(1);

    if (value != null) {

      valueCoder.registerByteSizeObserver(value, observer);

    }

  }



  /**

   * Overridden to short-circuit the default {@code StructuredCoder} behavior of encoding and

   * counting the bytes. The size is known (1 byte) when {@code value} is {@code null}, otherwise

   * the size is 1 byte plus the size of nested {@code Coder}'s encoding of {@code value}.

   *

   * <p>{@inheritDoc}

   */

  @Override

  protected long getEncodedElementByteSize(@Nullable T value) throws Exception {

    if (value == null) {

      return 1;

    }



    if (valueCoder instanceof StructuredCoder) {

      // If valueCoder is a StructuredCoder then we can ask it directly for the encoded size of

      // the value, adding 1 byte to count the null indicator.

      return 1 + ((StructuredCoder<T>) valueCoder).getEncodedElementByteSize(value);

    }



    // If value is not a StructuredCoder then fall back to the default StructuredCoder behavior

    // of encoding and counting the bytes. The encoding will include the null indicator byte.

    return super.getEncodedElementByteSize(value);

  }



  /**

   * {@code NullableCoder} is cheap if {@code valueCoder} is cheap.

   *

   * <p>{@inheritDoc}

   */

  @Override

  public boolean isRegisterByteSizeObserverCheap(@Nullable T value) {

    if (value == null) {

      return true;

    }

    return valueCoder.isRegisterByteSizeObserverCheap(value);

  }



  @Override

  public TypeDescriptor<T> getEncodedTypeDescriptor() {

    return valueCoder.getEncodedTypeDescriptor();

  }

}